Flame sensor testing for American Standard AUX040C924D3

[crosstalk]

We have just started the heating season where I live so I wanted to make sure my furnace is ready.  I need some help on technique for testing the flame sensor.  I have a microamp meter, but I can't figure out an easy way to connect it in series with the sensor.  Seems like a lot of trouble to open up the combustion chamber to connect the meter at the spade connector on the sensor.  Is it ok to run the furnace with the combustion chamber open?  Otherwise, it seems like I will have to cut the sensor wire and crimp some terminals in line to be able to get a reading.  I see some oxidation on the sensor but I'm not sure if I should clean/replace it yet.  Last season, I noticed a few ignition retries but never a lockout.

The ignitor has a resistance of 15.2 ohms (I think it's a model IGN00117 silicon nitride).  Also I noticed that the multi-wire connectors on the control board were not fully seated and locked (and I can't get them to lock).  It doesn't seem to be a problem (furnace is running) but I have never had this problem before--is it common for these not to seat?  Thanks for any help.

[applianceman18007260692]

You could remove the sensor and clean it with a dry brillo pad. Ain't no way to test it. Get another one to have on hand for just in case. Over last weekend, sat morning my furnace wouldn't lite at all. Was making a gurgling noise. I found water in the draft inducer and water all over the heater. The ac pan above was overflowing because the drain was stopped up and water was flowing into the furnace. I cleared the ac drain pipe. I dried everything out with a hair dryer and dumped the water out the draft inducer. I scrubbed the orifices with a soft brush. But did not need to clean the sensor believe it or not. Furnace is all good now. Dude I would not worry about it too much if it is clean dry and in working order.

[crosstalk]

Thanks for the reply.  Is the ignitor on this furnace pretty reliable or is it worth having a spare on hand?

[applianceman18007260692]

I would say it is pretty reliable but why take chances? Get a spare.

[ACtechGUY]

Hi There, There should never be a reason to replace the flame sensing rod.(except for when you bend it trying to test it!!!!) Clean off any oxides with sandpaper. That is it. The fame sensor is simply a bent piece of metal that conducts current via the flame to the control board.

NOW, your hot surface igniter (the thing that glows red) is a wear and tear item. Depending on which one you have the service life varies.

If the igniter kinda has a M shape to it, those tend to have a 5 to 10 year life span.

If it is shaped like a small bar then GREAT!! I have never seen one like that fail.

Hope that helps.

[Shootist]

I don't understand your wanting to "test" the flame sensor. I can assure you that if there is a problem with the sensor the furnace won't work.

[ACtechGUY]

You are very right. The only time I ever "test" anything to do with the flame sensing circuit is when something does not work.